1. Field of the Invention
This invention relates to an air bag inflation gas generator to feed gas for inflation of air bags such as air bags for absorbing collision shocks, life jackets, rafts, and escape chutes.
2. Description of the Prior Art
A prior shock absorber to protect a passenger car driver from shocks at collision accidents comprises an air bag, for example, having a capacity of 60 liters and a gas generator to inflate the air bag with gas. At a collision accident, explosives or other gas generating agents having a similar composition thereto, which are charged in the gas generator, are ignited and burnt to produce some gas. The air bag is instantaneously inflated by the resultant gas for driver protection against any collision shocks, which can avoid possible serious injury.
FIG. 13 shows a prior air bag inflation gas generator disclosed in the U.S. Pat. No. 4,296,084. In the drawing, the reference numeral 11 shows a combustion chamber containing a plurality of pellets of gas generating agent 13.
In the center of the combustion chamber 11, an igniter 15 and an ignition agent 17 are arranged to burn the gas generating agent 13. The combustion chamber 11 has also a combustion chamber filter 19 on its inner wall.
A plenum chamber 21 annularly surrounds the combustion chamber 11 and receives gas flow from the combustion chamber filter 19.
The plenum chamber 21 contains a gas filter (plenum chamber filter) 23 and further includes a plurality of gas outlets 25 to supply the gas flow from the gas filter 23 to an air bag.
In this type of air bag inflation gas generator, the ignition agent 17 burns when the igniter 15 is energized. The burning agent 17 in turn causes the gas generating agent 13 to burn and the resultant gas flows into the plenum chamber 21 through the combustion chamber filter 19 which is arranged on the inner wall of the combustion chamber 11. The gas is purified by the gas filter 23 in the plenum chamber 21 and flows into the air bag through the gas outlets 25. The air bag can be inflated completely within a very short time, for example, approximately 0.04 second.
That prior air bag inflation gas generator, however, has a housing body 27 comprising a covering member 29 and a housing cover 33 to form the combustion chamber 11 and the plenum chamber 21, and the covering member 29 and the housing cover 33 are screwed on each other through the engagement between an external thread 31 formed on the outer surface of the covering member 29 and an internal thread 35 formed on the inner surface of the cover 33. This housing construction increases not only the thickness of each portion where the thread 31 or 35 is formed, but the total thickness of the cover 33 and the covering member 29, resulting in a relatively large weight of the air bag inflation gas generator. In addition, the construction is an obstacle to providing a smaller gas generator.
For example, an air bag inflation gas generator to be installed in the steering wheel of an automobile has been highly requested to be lighter and smaller in order to improve the appearance and simplify the installation job. Nevertheless, such request has hardly been fulfilled due to the disadvantages described above.
In that prior air bag inflation gas generator, a large number of granules or pellets of gas generating agent 13 are charged in the combustion chamber 11. This produces large voids and as a result, requires a large size of the combustion chamber 11. This disadvantage also prevents production of smaller gas generators.
In addition, the prior air bag inflation gas generator employs a cartridge 28 to contain the gas generating agent 13 in the combustion chamber 11 and the cartridge 28 has a through hole 30 into which a plug 32 is fastened to support the igniter 15. To seal the cartridge 28 completely, therefore, a complicated sealing mechanism is required.
More specifically, if the gas generating agent 13 is moisturized when the air bag inflation gas generator installed in the steering wheel of an automobile is moisturized, the gas generator may not operate properly at a collision. Therefore, complete sealing of the gas generating agent 13 and the ignition agent 17 is highly requested.
Besides, the gas filter 23 which is installed in the plenum chamber 21 to filter the generated gas hardly provides enough cooling, dispersion and filtration of the combustion gas. To solve this problem, the prior air bag inflation gas generator is required to have a gas filter which ensures such functions.
Moreover, the gas filter is required to have low ventilation resistance to cool, disperse, and filter combustion gas enough because it is very hot and passes through it into the air bag at a high speed.